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I was in a shop last week and the owner has been helping a customer with a Garrett Stage 2 vs. 3 comparison. He also wants to try the Stage 3 on his highly modded truck. He knew I know a Garrett engineer so asked me to find out if he could leave the water cooling kit off to make the swap easier and faster for a short-term test. He had heard if oil pressure is over 40 the water cooling may not be necessary, but that didn't sound right to us. These ball bearing turbos use an oil inlet restrictor because the ball unit doesn't need or like as much oil as a journal bearing unit. Spools faster with less oil windage. So that probably means less oil cooling. So here is the answer from Garrett if anybody is interested:

“A water-cooled turbocharger can live for a time without water lines plumbed; that being said, any turbocharger with water ports was designed with water cooling in mind and its lifetime will be shortened without water. We always recommend running water lines to a water-cooled turbo since the work involved is usually minimal and the consequences of failure due to an overheated bearing will be great. How long it will last is dependent on many factors, including exhaust gas temperatures, duty cycle (how hard the turbo is run over its lifetime…racing, street use, towing, etc), oil pressure, oil quality, oil temperatures, and shutdown procedures. The water cooling around the bearing helps during all operating conditions but gives its greatest benefits during hot shutdowns. The water will “thermal siphon” and continue to pull heat out of the turbocharger even after the engine has been shut down and the water pump is no longer pumping. This will keep the exhaust heat stored in the turbine housing from coking the oil in the turbocharger and potentially damaging the bearing and turbine-side oil seal.

We know that some people do have success without running water lines, but looking at the cost of running lines vs. the benefits, why take the risk? If there is no concern about longevity or durability, and the turbocharger will only be used for a short time and then discarded, then deleting the water cooling will not have any ill effects. However, if the turbocharger will be expected to remain in service at elevated power levels for years to come, water lines need to be hooked up. Most who buy Garrett GT ball-bearing turbochargers are expecting them to last and wouldn’t consider an inexpensive / off-brand / knock-off turbocharger, so it is in their best interest to take the extra small steps required to plumb water into and out of the center housing. In the specific case of the Dodge Cummins PowerMax kits, all water lines needed are included in the kits. These went through an intensive design and qualification process and are designed to prevent premature turbocharger failures due to overheating. They should not be difficult to install and remove and should not require much adjustment; every individual vehicle is slightly different but in most cases a small amount of fine-tuning by gently bending the hard lines is all that is required for fitment on a particular truck.”
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